Interlayer Magnetophononic Coupling in MnBi,Te4

R. Schaller, H. Padmanabhan, H. Wang, M. Wetherington, V. A. Stoica, S. H. Lee, Z.Q. Mao, V. Gopalan, M. Poor, P. Kim, R. Averitt, N. Z. Koocher, D. Puggioni, M. Gu, J. M. Rondinelli, X. Shen, A. H. Reid, A. M. Lindenberg, X. Wang

Magnetism in quantum materials creates a fertile ground for the Al (a. u.) exploration of fundamental spin-based phenomena, with applications in spintronics, 10.3 magnetic memory, and quantum information technology. This is exemplified by the recent development of magnetic topological materials. As with other functional materials, the identification of accessible coupling pathways to the foremost degree of freedom is key to enabling new fundamental and technological breakthroughs. In Magnetic field (T) HeN 0.2 MnBiTes, a layered intrinsic antiferromagnetic topological insulator, we found sub- picosecond coherent magnetophononic coupling. Specifically, light-induced displacive 30 excitation of phonons coherently modulates magnetism at terahertz frequencies, 40 50 Frequency (cm*) 60 90 100 110 Frequency (cm" 120 130 orders of magnitude faster than traditional techniques such as strain or magnetic fields. Moreover, we also used Raman spectroscopy to reveal magnetic control derives from strong optical phonon exchange coupling. These results are buttressed pump (1.55 eV) with insights obtained from MeV ultrafast electron diffraction experiments. probe (1.2 eV Interestingly, we found that the experimentally observed magnetic response speed belies expectations based on an equilibrium description of the exchange interaction. Thus, we demonstrated the first step towards achieving ultrafast control of magnetic -0 topological phases and challenged the prevailing ideas of nonequilibrium magnetism Residual AR/R (normalized fits) 0.2 at femtosecond timescales.